The present invention relates to an apparatus for performing solid-liquid separation by water treatment.
Heretofore, as a method for performing the solid-liquid separation of water to be treated having a high turbidity such as a water purification treatment, a sewage disposal treatment, a waste water treatment or an industrial waste water treatment, there have been carried out sand filtration, gravity precipitation and the like. In the solid-liquid separation by any of these methods, however, there are inconveniences that the water quality of the treated liquid is insufficient on occasion and that a vast site is required for the solid-liquid separation.
As techniques for eliminating such inconveniences, various methods have nowadays been investigated in which the solid-liquid separation of the water to be treated is carried out by the use of a membrane module provided with a separation membrane such as a precise filter membrane or an ultrafilter membrane. The filtration treatment of the water to be treated by the use of the separation membrane permits obtaining the treated liquid having a high water quality.
In the case that the solid-liquid separation of the water to be treated is done by the use of the separation membrane, the clogging of the pores in the surface of the separation membrane progresses with the continuation of the filtration treatment by suspended substances, so that a filtration flow rate deteriorates or a pressure difference between the membranes increases. In order to eliminate such conditions, a gas diffuser pipe is disposed under the membrane module, whereby air is diffused through the gas diffuser pipe to swing the separation membrane and to thereby separate the suspended substance from the membrane surface.
However, even in the system in which waste water is filtered through the membrane module, it is difficult to uniformly continuously apply air bubbles discharged from the gas diffuser device to the separation membrane during a long-term operation. In consequence, the suspended substance clogs the pores in the surface of the membrane, so that the filtration flow rate deteriorates, and hence, there is an inconvenience that a maintenance operation is often required to recover the deteriorated filtration flow rate.
For the resolution of this inconvenience, Japanese Patent Application Laid-Open No. 117647/1997 has suggested a method in which the amount of air to be fed to the gas diffuser device is controlled to inhibit the clogging of the gas diffusion pores, but the gas diffusion pores themselves are not considered at all, so that the effect of uniformly washing the membrane module is poor.
Furthermore, as disclosed in Japanese Patent Application Laid-Open No. 192662/1997, there has been suggested a system in which the gas diffuser device alone can easily be removed from a treating tank, but also in this system, the gas diffuser pores themselves are not considered at all, so that the clogging of the gas diffuser pores is allowed and hence there is an inconvenience that a maintenance operation of washing the clogged gas diffuser device is often required.
The present invention has been developed to solve the above-mentioned inconveniences, and an object of the present invention is to provide a water treatment apparatus in which gas discharge holes of a gas diffuser device are scarcely clogged even when filtration is carried out for a long period of time, and as a result, the clogging of the pores in the surface of a membrane with a suspended substance is inhibited and stable filtration is continuously possible for a long time.
That is to say, the first aspect of the present invention is directed to a water treatment apparatus in which a membrane separation device is disposed above a gas diffuser device arranged in a treating tank, wherein diameters of gas discharge holes formed in the gas diffuser device are within a range of 1 to 10 mm, and a relational expression of 20 less than X/Y less than 300 is satisfied wherein X is a sectional area (cm2) of the membrane separation device in a horizontal direction, and Y is the number of the gas discharge holes of the gas-diffuser device.
The second aspect of the present invention is directed to a water treatment method which comprises the step of filtering water to be treated by a membrane separation device while air is continuously or intermittently diffused through a gas diffuser device; diameters of gas discharge holes formed in the gas diffuser device being within a range of 1 to 10 mm; the membrane separation device being disposed above the gas diffuser device in which a relational expression of 20 less than X/Y less than 300 is satisfied wherein X is a sectional area (cm2) of the membrane separation device in a horizontal direction, and Y is the number of the gas discharge holes of the gas diffuser device.